The field of the present invention is apparatus for dispensing and safely controlling bulk materials such as petroleum coke or other analogous products.
Facilities for the manufacture of bulk materials such as petroleum coke and the like usually include means for producing and storing the produced output prior to shipment. In the specific case of petroleum coke, high boiling petroleum fractions are processed in one or more large volume drums. FIG. 1 illustrates a typical petroleum coke production facility, commonly known as a delayed coker, comprising a pair of coke drums mounted in a concrete and/or steel support structure. The drums are positioned above an apron having openings forming the entrance to coke chutes extending below the apron.
In the petroleum coking process high boiling (greater than 425.degree. C.) hydrocarbons are heated to about 500.degree. C. and put into a large drum where thermal cracking of the molecules takes place. This thermal cracking produces small molecules which exit the drum, and larger molecules which remain in the drum to form a solid residue known as petroleum coke. When one drum fills up with the residue, the inlet hydrocarbon stream is switched to an empty drum. The full drum is then steamed to remove residual hydrocarbon and then the coke mass within the drum is cooled by quenching with water. After cooldown to about 95.degree. C. the quench water is drained, the coke drum bottom and top covers (heads) are removed, and the coke is removed using high pressure water jets. This process is typically known as delayed coking. The heads are then replaced and the empty drum is available for the feed switch when the other drum fills up. The process is continued using this alternating drum technique.
As shown in FIG. 1, the outlets of the coke drums are closed during the coke production process step by means of steel drumheads that are secured to the drums by a plurality of bolts disposed about the circumference of the coke drum outlets. For a typical coke production facility, the drumheads are approximately seven feet in diameter and five inches thick.
The coke drums are alternately unheaded on a time schedule depending on the charge rate of the unit, the coke yield and the number of drums utilized. In current practice the drumheads are manually removed ("unheaded") by operators who remove the drumhead bolting using pneumatic impact wrenches. In order to maintain coke production schedules and a steady coker unit output stream, it is essential that the unheading operation be safely and expeditiously performed. In the production facility of FIG. 1, unheading typically takes about ten to thirty minutes.
During the unheading of the coke drums of FIG. 1, the drumhead is supported in place by an adjustable unheading cart that is typically mounted on tracks. After the head bolts are removed, the drumhead is lowered from the coke drum outlet. The head and the cart are then rolled to the side to fully expose the open outlet. A collapsible chute is hoisted from the deck to tie the coke drum outlet to the coke chute in the drum support structure to prevent spillage during coke removal. The coke is then "cut" from the drum by (a) high pressure water jet(s). This operation of removing coke from the drum takes around two to six hours. The drum is subsequently reheaded by reinstalling the head bolts. The reheading operation takes around fifteen to forty minutes.
The above-described practice has worked relatively satisfactorily over the years for the production of "sponge coke", which forms a mass inside the coke drum that will normally support itself and remain intact, even with the drumhead removed. However, if, as occasionally occurs, the coke drum fails to properly drain off water used for quenching the hot coke, a combined hydrostatic and coke load with a total weight around 100 tons could act on the drumhead, rendering bolt removal difficult and subjecting the unheading cart to excessive loads. An inadequate drain may also result in an uncontrolled discharge from the drum of high temperature (80.degree.-95.degree. C.) water, steam, coke slurry or coke particle streams as the drumhead is being lowered, subjecting personnel to a hazardous situation.
With the use of certain types of feed stocks which are becoming more prevalent, "shot coke" is produced in lieu of sponge coke. "Shot coke" has the consistency of small BB pellets which may or may not be agglomerated into large "coke balls." "Shot coke" and the associated "coke balls" may not form a self supporting mass in the coke drum and may therefore behave as a liquid to impose high hydraulic load on the head similar to water. This fluid-like behavior of the "shot coke" will force the drumhead down with considerable force onto the coke drum unheading cart. The coke can also flow out with significant velocity from the gap between the drum and the partially lowered head, a potential hazard to operating personnel, and, if the unheading cart is pinned in place by the partially lowered head, may spread onto the unheading deck and equipment below the deck. The coke's fluidity also increases the potential for inadequate drainage of quench water by its tendency to plug the drainage outlets, again leading to excessive loads on the drumhead and the unheading cart. Thus, "shot coke" production entails the dual problems of safety due to excessive and uncontrolled discharge, and the disruption of production feed cycles due to excessive drumhead and unheading cart loading.
Accordingly, an alternative method of removing a coke-drumhead, providing the ability to withstand the high bottom head loads developed in the case of an inadequate quench water drain, controlling and directing hot water and particulate discharge via the bottom head, enabling the unheading operators to distance themselves from the coke drum outlet during drumhead removal and maximizing coke production throughput, would be desirable.